ANSWER
A. 12
EXPLANATION
From the stem-and-leaf plot, the trees that are between 610 inches tall and 640 inches tall are:
613,616,622,622,624,625,631,631,633,637,637,and 638.
Counting the number of trees gives 12 of them.
Therefore, the number of trees that are between 610 inches tall and 640 inches tall is 12.
The correct answer is A.